1. Field of the Invention
The present invention relates to polysaccharide derivatives having specific numbers of hydrophilic functional groups and nitrate groups; the neutralized polysaccharide derivatives; compositions used as a binder (hereinafter referred to as binder compositions) comprising the neutralized polysaccharide derivatives, water and minimum amount of organic solvents; and compositions used as a vehicle (hereinafter referred to as vehicle compositions) comprising the binder composition and a water-dispersible resin and/or a water-soluble resin.
2. Description of Related Art
It is know that cellulose nitrate is often used for printing compositions, paper coatings, fabric surface coatings, and functional coatings such as magnetic coatings and conductive paste for its excellent properties such as pigment dispersibility, drying characteristic, compatibility with various types of coating resins, thixotropic properties, heat resistance and blocking resistance. In most uses mentioned above, cellulose nitrate is used for coatings containing organic solvents wherein organic solvents are evaporated to form films. The evaporated organic solvents cause air pollution, a deterioration of working environment, danger of fires, etc. Therefore, various types of aqueous coatings have been developed in place of the coatings containing organic solvents.
As representative examples of the aqueous coatings, coatings comprising a water-soluble resin and/or a water-dispersible resin such as an acrylic copolymer and a stylene-maleic acid copolymer are known. However, they have not been widely used except for building in the form of emulsion, since their properties are not statisfactory. Carboxymethylcellulose (sometimes referred to hereinafter as CMC), hydroxymethylcellulose etc. which are known as water-soluble polysaccharides do not have sufficient compatibility with resins for aqueous coatings and pigment dispersibility.
Consequently, there has been strong demand for a novel vehicle composition containing a composition having properties as those of cellulose nitrate, but not capable of causing air pollution, a deterioration of working environment, danger of fires etc. in use.
For the purpose of solving the above problems, it has been proposed to use cellulose nitrate in the form of (i) lacquer emulsion and (ii) water dispersion of cellulose nitrate/acrylic copolymer. The former case (i) includes an aqueous dispersion known as aqueous coatings for leather, which is obtained by dissolving cellulose nitrate in an organic solvent with a plasticizer and/or resins capable of being dissolved in organic solvents, and dispersing the resultant in water in the presence of an emulsifier. However, the aqueous dispersion has substantially the above-mentioned problems, because it contains a large quantity of organic solvents.
The latter case (ii) includes an aqueous dispersion disclosed in Japanese Patent Application Laid-Open Nos. 80358/1983, 69214/1983 and 195172/1985. The aqueous dispersion can be obtained by dissolving cellulose nitrate in an acrylic monomer or oligmer, and dispersing the resultant in water with an emulsifier, followed by subjecting to a radical polymerization. However, cellulose nitrate being used in the aqueous dispersion is essentially hydrophobic and the aqueous dispersion contains a large amount of organic solvents. Consequently, the aqueous dispersion still has the above-mentioned problems.
Polysaccharide derivatives having carboxyl groups and nitrate groups are disclosed in the following specifications. Japanese Patent Application Laid-Open No. 71342/1984 discloses water dispersible compositions comprising an oil phase containing oxidized nitrocellulose having 2 mg equivalent/100 g or more of carboxyl groups and a low water-soluble solvent capable of dissolving the oxidized nitrocellulose; and an water phase having water as a main component. The oxidized nitrocellulose having anionic hydrophilic functional groups and hydrophobic ester functional groups can lessen the amount of an emulsifier used. Consequesntly, the heat resistance and water resistance of the obtained films are improved, but air pollution, a deterioration of working envioronment, danger of fires, etc. are not sufficiently improved since the compositions contain a large amount of organic solvents. Also, the oxidized nitrocellulose is substantially insoluble in water or a mixture of water and organic solvents since the amount of the hydrophilic functional groups is not large enough.
Crosslinked CMC having carboxymethyl ether groups and nitrate groups for solid propellants is proposed in U.S. Pat. No. 3,638,698 and the process thereof is proposed in German Patent No. 2,737,699. However, they do not teach the use in aqueous coatings at all.
Further, Rumanian Patent No. 96819 discloses a process for producing polysaccharide derivatives having carboxymethyl ether groups and nitrate groups, and the products obtained thereby to be used as a stabilizer in alkaline suspensions or as a thickening agent. However, there is no disclosure regarding the use of the product in aqueous coatings.
Thus, conventional coatings, which involve the above-mentioned problems, have not been adequate for aqueous coatings.